1. Field of the Invention
The present invention relates to an apparatus and a method for controlling a variable valve timing mechanism (Valve Timing Control System: VTC), which changes rotational phase of a cam shaft with respect to a crank shaft, thereby changing a valve timing (open and close timing) of at least one of an intake valve and an exhaust valve.
2. Description of Related Art
In order to change valve timing according to an engine operating condition, a VTC is known to public, which changes a rotational phase of a cam shaft with respect to a crank shaft by an actuator. With respect to an engine having a VTC, Japanese Laid-open (Kokai) Patent Application Publication No. 2009-13975 discloses a technique of changing a valve timing so as to be suited to start of an engine when the engine is stopped, thereby ensuring an engine-start performance. Since a VTC cannot change the valve timing when the engine is stopped, on detecting rotation of a crank shaft, a feedback-control of the cam shaft is started based on deviation of an actual angle from a target angle.
Along with rotation of the cam shaft, a VTC attached to the tip of the cam shaft receives an alternate torque (cam torque) constituted by a reaction force of a valve spring and an inertia force of the mass of a moving portion. In the method of starting a feedback-control on detecting rotation of the crank shaft, since there may be a delay of starting the feedback-control from a timing at which the engine is actually started, the valve timing may significantly deviate from a target angle by the time of starting the feedback-control due to the cam torque at the engine starting.